DE69229513T2 has disclosed that it is possible to protect silicon-containing ceramic surfaces from oxidation by means of a silicon oxide layer with an aluminum oxide as an intermediate layer. In this connection, the aluminum oxide intermediate layer is needed as a barrier against oxygen diffusion.
EP0880607B1 describes an oxidation protection layer for high-melting-point materials, which is composed of suicides or aluminides in which a reaction-preventing layer is necessarily provided between the oxidation protection layer and the high-melting-point material. The reaction-preventing layer is an oxide layer, preferably a hafnium or zirconium oxide.
U.S. Pat. No. 5,741,596A discloses an oxidation protection layer for metallic substrate surfaces. The oxidation protection layer is composed of three different layers; the first layer contains essentially mixtures of oxides, the second layer is composed of aluminum oxide and silicon carbide, and the third layer closest to the surface is composed of silicon oxide and admixtures of other oxides and silicon carbide. In addition to the oxidation protection effect, this layer should also have higher emittance and reduced catalytic activity.
WO2005051866A1 discloses an oxidation barrier for silicon-containing ceramics, which are used in was turbines and which are exposed to hot gases with high percentages of water vapor. Without oxidation protection, oxide formation occurs on the surface of silicon nitride-based and silicon carbide-based ceramics, which results in a loss of material due to erosion. The protective coating is composed of a diffusion barrier coating, another layer serving as an oxidation barrier made of scandium disilicate, another layer that protects against environmental influences composed of titanium oxide and scandium silicates and -oxides, and finally a thermal protective coating that contains stabilized zirconium oxide. This application describes that the different layers are necessary on the one hand to prevent oxygen diffusion into the substrate and on the other hand, to avoid the formation of a mechanically unstable oxide on the surface. It also refers to the problem that for example a thin oxide composed of SiO2 constitutes a good diffusion barrier, but it must be thin enough so that cracks do not form in this layer. In principle, this patent very clearly describes the complicated set of problems involved in optimizing an oxidation barrier layer and the complicated interrelationships that must be taken into account when adapting mechanical properties of protective coatings to one another and how their different oxidation capacities must be taken into account so that an effective and stable oxidation protection layer can be achieved.